Halogenated aromatic polyesters based on bisphenols may be prepared by interfacial polymerization techniques. In accordance with typical interfacial polymerization procedure of the prior art, the reactants are present in different liquid phases which are immiscible and which, in the preparation of these polymers, constitute two solvent media. Thus, a bisphenol is dissolved in one solvent medium, and an aromatic diacylhalide is dissolved in a second solvent medium immiscible with the first. Any necessary catalyst such as quaternary ammonium salt or phosphonium salt is generally added to the aqueous phase. The organic phase is then rapidly added to the aqueous phase with vigorous agitation.
Although it is preferred to add the organic phase containing the mixture of acid chlorides to the aqueous phase containing the bisphenol in the interfacial polymerization procedures of the prior art, it has also been recognized that the polymerization may be carried out by inverting the order of addition of reactants and adding the aqueous phase to the organic phase. (See U.S. Pat. Nos. 3,274,290 and 3,278,640, as well as U.S. patent application Ser. No. 686,190, filed May 13, 1976.) In either case, however, both phases are rapidly combined with vigorous agitation regardless of the order of addition. Thus, the prior art techniques fail to suggest a slow, controlled rate of addition of the aqueous phase to the organic phase and the advantages which result therefrom when carried out in accordance with the presently claimed invention.
In the past it has been very difficult to obtain by interfacial polymerization, polyesters of the type described herein which possess the high molecular weights required in fiber spinning techniques. Thus, the procedures and techniques of the prior art have relied upon catalysts such as those disclosed in U.S. Pat. No. 3,100,698 and U.S. Pat. No. 3,234,167 to achieve and ensure high molecular weight products. It has been standard procedure to add the catalyst to the aqueous phase prior to mixing with the organic phase. Alternative and less preferred methods of utilizing the catalyst include adding the catalyst to the reaction mixture initially or during the course of polymerization or alternatively adding it intermittently during the reaction. However, the procedures of the prior art fail to suggest the addition of the catalyst to the organic phase prior to the addition of the aqueous phase thereto and the advantages which result therefrom when utilized in accordance with the present invention.
It has been observed that certain halogenated aromatic polyesters of the type defined herein will evidence a bimodal molecular weight distribution and will therefore substantially always possess a low molecular weight fraction comprising a substantial portion of the total polymer (e.g., about 15 to 20% by weight) when prepared by the above described interfacial polymerization processes of the prior art. The presence of the low molecular weight fraction (e.g., that portion of the polymer having molecular weight not greater than about 8000) gives rise to certain properties, such as, poor solvent resistance, which become undesirable in certain environments such as dry cleaning and/or dyeing operations.
The present invention offers a method for substantially reducing the amount of low molecular weight fraction which accompanies the formation of certain halogenated aromatic polyesters prepared by the standard interfacial polymerization (1) by inverting the order of addition of one phase to the other, i.e., by adding the aqueous phase to the organic phase, (2) by controlling the rate of addition of the aqueous phase to the organic phase and (3) by adding the catalyst to the organic phase prior to the addition of the aqueous phase thereto. The halogenated aromatic polyesters prepared in accordance with the presently claimed invention possess a molecular weight distribution similar to that obtainable from a solution polymerization technique at a substantial savings in cost.
Interfacial polymerization is more economically favorable than the solution polymerization technique because of the former technique's ability to utilize less expensive bases such as sodium hydroxide as an acid acceptor rather than the more expensive triethylamine required in the latter process. The use of such bases as triethylamine necessitates additional removal and recycle steps to collect and conserve the expensive compounds thereby further increasing the cost of the process. In contrast, polyesters prepared by interfacial polymerization are easily washable. Further advantages of the present invention include shorter reaction times than those utilized in solution polymerization as well as the ability to use water as a portion of the reaction mixture which reduces the quantity of organic solvents from that utilized in solution polymerization thereby also reducing solvent recovery costs.
It is therefore an object of the presently claimed invention to provide a relatively inexpensive process for the preparation of high molecular weight halogenated aromatic polyesters of the type disclosed which possess a narrow molecular weight distribution.
These and other objects as well as the scope, nature and utilization of the invention will be apparent to those skilled in the art from the following description and appended claims.